Coagulation Factor IX
The blood coagulation factor IX (F.IX) plays a central role in the coagulation cascade. F.IX is a trypsin-like vitamin K-dependent serine protease that circulates in the plasma as a single chain inactive zymogen (DiScipio et al., 1977; Davie et al., 1991). Factor IX is activated by either factor XIa or by factor VIIa-tissue factor in a Ca2+ dependent manner. The activation requires cleavage of two peptide bonds by either the activated factor VII (F.VIIa)-tissue factor complex or activated factor XI (F.XIa) (Fujikawa et al., 1974; Lindquist et al., 1978) to remove a 35-residue activation peptide.
F.IX is a multi-domain protein. An N-terminal γ-carboxy glutamic acid (GLA) domain is followed by two epidermal growth factor-like (EGF) repeats, the activation peptide (AP) and a C-terminal serine protease domain with a trypsin-like active site (DiScipio et al., 1978). This domain structure defines the serine protease family of clotting factors (Furie and Furie, 1988), including also factor II (F.II), factor VII (F.VII), factor X (F.X), factor XI (F.XI), factor XII (F.XII), and protein C (PC). Within this family, F.IXa has unique proteolytic properties. Complex formation of F.IXa with F.VIIIa on a phospholipid surface increases reactivity against the natural substrate F.X 106-fold (Duffy and Lollar, 1992), while virtually no cleavage of peptides with corresponding F.X sequences was observed (McRae et al., 1981).
Activated factor IX (F.IXa) then activates factor X (F.X) in a reaction that is dependent on the presence of calcium ions, a membrane surface (phospholipid), and a nonenzymatic protein cofactor, activated factor VIII (F.VIIIa) (Davie et al., 1991).
The importance of F.IXa in hemostasis is reflected by the occurrence of the bleeding disorder hemophilia B in individuals carrying mutations in the F.IX gene (Gianelli et al., 1998). F.IXa displays only very little proteolytic activity against natural or synthetic substrates in the absence of its cofactor F.VIIIa. Binding of F.VIIIa results in a 106-fold increase in proteolytic activity for F.X, whereas the activity with peptidic substrates remains less affected (Duffy and Lollar, 1992; McRae et al., 1981). The latter substrate-dependent activity of F.IXa modulation is similarly observed for the related coagulation enzymes activated PC (co-factor Protein S), F.Xa (co-factor Factor Va), F.VIIa (cofactor tissue factor), and FIIa (co-factor thrombomodulin), which in the presence of their cofactors, achieve a significant activity or specificity change with their natural substrates. (Mann et al. 2003). All coagulation serine proteases share extensive structural and functional homology.
Furthermore, the coagulation factors IXa (F.IXa) and Xa (F.Xa) both cleave natural substrates effectively only with a cofactor at a phospholipid surface. Hopfner et al. (1997) investigated variants of truncated F.IXa (rf9a) and F.Xa (rf10a) in E. coli to identify determinants of the difference in the amidolytic activity of F.IXa which is 104-fold lower than that of F.Xa. Based on the crystal structures of F.IXa and F.Xa four characteristic active site components (namely Glu219, the 148-loop, Ile213, the 99-loop, based on chymotrypsin numbering) were subsequently exchanged between rf9a and rf10a. Furthermore, combining all four mutations essentially introduced F.Xa properties into rf9a, i.e. the amidolytic activity was increased 130-fold with F.Xa substrate selectivity.
Enzymatically, F.IXa is characterized by its very low amidolytic activity that is not improved in the presence of cofactor, factor VIIIa (F.VIIIa), distinguishing F.IXa from all other coagulation factors. Activation of the F.IXa-F.VIIIa complex requires its macromolecular substrate, factor X (F.X). The 99-loop positioned near the active site partly accounts for the poor activity of F.IXa because it adopts a conformation that interferes with canonical substrate binding in the subsites S2-S4. Sichler et al. (2003) disclose that residues Lys-98 and Tyr-99 (chymotrypsin numbering) are critically linked to the amidolytic properties of F.IXa. Exchange of Tyr-99 with smaller residues resulted not only in an overall decreased activity but also in impaired binding in S1. Replacement of Lys-98 with smaller and uncharged residues increased activity. Simultaneous mutagenesis of Lys-98, Tyr-177, and Tyr-94 (rf9-Y94F/K98T/Y177T, chymotrypsin numbering)) produced an enzyme with 7000-fold increased activity and altered specificity towards factor Xa. Sichler et al. (2003) concluded, that these residues account for the low factor IXa activity. Sichler et al. (2003) concluded, that this triple mutant rf9-Y94F/K98T/Y177T (chymotrypsin numbering) probably mimics the conformational changes that are physiologically induced by cofactor and substrate binding.
Hemophilia
The best-known coagulation factor disorders are the hemophilias. Hemophilia is the name of a family of hereditary genetic disorders that impair the body's ability to control blood clotting, or coagulation. Haemophilia A, the most common form, is caused by a mutation of the factor VIII (F.VIII) gene, leading to a deficiency in F.VIII. The inheritance is X-linked recessive; hence, males are affected while females are carriers or very rarely display a mild phenotype. 1 in 5,000 males are affected. Hemophilia B, also known as factor IX (F.IX) deficiency, is the second most common type of hemophilia, but hemophilia B is far less common than hemophilia A.
These genetic deficiencies may lower blood plasma clotting factor levels of coagulation factors needed for a normal clotting process. When a blood vessel is injured, a temporary scab does form, but the missing coagulation factors prevent fibrin formation which is necessary to maintain the blood clot. Thus a haemophiliac does not bleed more intensely than a normal person, but for a much longer amount of time. In severe haemophiliacs even a minor injury could result in blood loss lasting days, weeks, or not ever healing completely. The critical risk here is with normally small bleeds which due to missing F.VIII take long times to heal. In areas such as the brain or inside joints this can be fatal or life debilitating. The bleeding with external injury is normal, but incidence of late re-bleeding and internal bleeding is increased, especially into muscles, joints, or bleeding into closed spaces. Major complications include hemarthrosis, hemorrhage, gastrointestinal bleeding, and menorrhagia.
Though there is no cure for haemophilia, it can be controlled with regular infusions of the deficient clotting factor, i.e. F.VIII in haemophilia A or F.IX in haemophilia B.
In western countries, common standards of care for hemophilia fall into one of two categories: (i) prophylaxis or (ii) on-demand. Prophylaxis involves the infusion of coagulation factor on a regular schedule in order to keep clotting levels sufficiently high to prevent spontaneous bleeding episodes. On-demand treatment involves treating bleeding episodes once they arise.
However, some haemophiliacs develop antibodies (inhibitors) against the replacement factors given to them, so the amount of the factor has to be increased or non-human replacement products must be given, such as porcine F.VIII or modified variants thereof, see e.g. WO 01/68109 A1 (Emory University).
If a patient becomes refractory to replacement coagulation factor as a result of circulating inhibitors, this may be overcome with recombinant human factor VII (NovoSeven®), see also EP 1 282 438 B1 and EP 1 282 439 B1 (Novo Nordisk). A limitation of this approach so far is the short half life of factor VIIa (2 to 3 hours) compared to factor VIII (10 to 14 hours) or factor IX (18 to 30 hours), respectively and depending on the preparation, which makes prophylactic therapy with factor VIIa difficult. Further, the risks of using an already activated protease, like factor VIIa, over prolonged time intervals might carry risks, including thrombotic risks, risks through constant activation of the vascular endothelium and vessel damage, risk of pro-coagulant signalling which could promote tumor growth or metastasis, etc.
WO 02/40544 A2 discloses mutant human factor IX comprising mutations in the heparin binding domain, which decrease the affinity of the mutant human F.IX for heparin compared to wild type F.IX, and their use in the therapeutic intervention of hemophilia B.
Gene Therapy
Hemophilia is ideal for a gene therapeutic approach since the required coagulation is circulating in the blood stream and may therefore be expressed basically everywhere in the body. Further, studies with prophylactic treatment of patients with a severe form of the disease have demonstrated that a minimal elevation of circulating coagulation factor above 1% can already improve the clinical outcome and avoid the majority of lesions caused by the disease, i.e. joint destruction. Several gene therapy approaches have been developed, but testing is still in the early clinical stages. The most promising approaches are currently for the treatment of hemophilia B with adeno-associated viral vectors (AAV).
Intramuscular injection AAV to skeletal muscle of humans with hemophilia B is safe, but higher doses are required to achieve therapeutic factor IX levels. However, dose escalation is not possible in this approach, since the risk of the formation of inhibitory antibodies depends on the amount of F.IX antigen expressed in the muscle per injection site. Estimation in a hemophilia B dog model let to the conclusion, that more then 400 intramuscular injections would be necessary to obtain F.IX expression levels of around 1% in humans (Arruda et al., 2004). This procedure, therefore, is not applicable to humans. The efficacy of this approach is hampered by the retention of F.IX in muscle extracellular spaces and by the limiting capacity of muscle to synthesize fully active F.IX at high expression rates. To overcome these limitations, Schuettrumpf et al. (2005) constructed AAV vectors encoding F.IX variants for muscle- or liver-directed expression in hemophilia B mice. Circulating F.IX levels following intramuscular injection of AAV-F.IX-K5A/V10K (F.IX numbering), a variant with low-affinity to extracellular matrix, were 2-5 fold higher compared with wild-type (WT) F.IX, while the protein-specific activities remained similar. Expression of F.IX-R338A generated a protein with 2- or 6-fold higher specific activity than F.IX-WT following vector delivery to skeletal muscle or liver, respectively. F.IX-WT and variant forms provide effective hemostasis in vivo upon challenge by tail-clipping assay. Importantly, intramuscular injection of AAV-F.IX variants did not trigger antibody formation to F.IX in mice tolerant to F.IX-WT. Besides of the mentioned R338A variant, first described by Chang et al. (1998), another variant, V86A, with higher specific F.IX activity has been described (Chang et al. 2002).
The application of gene therapy strategies for hemophilia A in comparison to hemophilia B is further complicated by the higher immunogenicity and the bigger size of the F.VIII compared to F.IX.
Thus, there is a need in the art for providing improved means and methods for the treatment and/or prophylaxis of bleeding disorders, in particular hemophilia A and/or B.
Thus, the present invention aims to improve the methods and means for the treatment and/or prophylaxis of bleeding disorders as present in the prior art and it is, thus, an objective of the present invention to provide improved methods and means which allow for an effective, specific and targeted treatment and/or prophylaxis of bleeding disorders, in particular hemophilia A and/or B.
According to the present invention this object is solved by providing a variant of a vitamin K-dependent serine protease of the coagulation cascade wherein the variant is characterized in that it has clotting activity in absence of its cofactor.
The coagulation factors VII (F.VII), IX (F.IX) and X (F.X) as well as the cofactor inhibitor protein C (which degrades the co-factors F.Va and F.VIIIa) and thrombin are vitamin K-dependent serine proteases of the coagulation cascade. Vitamin K is an essential factor to a hepatic gamma-glutamyl carboxylase that adds a carboxyl group to glutamic acid residues (in the Gla-domain) on factors II (thrombin), VII, IX and X, as well as protein S, protein C and protein Z.
As discussed above, the serine protease family of clotting factors, which includes factor II (F.II), factor VII (F.VIII), factor IX (F.IX), factor X (F.X), and protein C (PC), is defined by a specific domain structure (Furie and Furie, 1988).
Serine proteases are characterised by the presence of a serine residue in the active site of the enzyme. The mentioned proteins circulate in a zymogene form and are activated by cleavage of an activation site. There is great homology between all vitamin K-dependent coagulation proteases. Several of them exhibit the increase in activity only assembled in a complex consisting of the protease, cofactors and phosphlipid membranes. The molecular effect of cofactor binding and binding sites are similar among these proteins. The latter substrate-dependent activity of F.IXa modulation is similarly observed for the related coagulation enzymes activated PC (co-factor Protein S), F.Xa (co-factor Factor Va), F.VIIa (cofactor tissue factor), and FIIa (co-factor thrombomodulin), which in the presence of their cofactors, achieve a significant activity or specificity change with their natural substrates substrates. (Hockin et al. 2002).
Thus, a variant of a vitamin K-dependent serine protease of the coagulation cascade is preferably selected from a variant of factor VII (F.VII), factor IX (F.IX), factor X (F.X), protein C or thrombin.
The term “variants” preferably refers to amino acid substitution, addition (insertion) or deletion variants or derivatives of the naturally occurring protein. Variants comprise furthermore an amino acid sequence comprising modified amino acid(s), unnatural amino acid(s) or peptidomimetic(s) or further compounds which can mimic a peptide backbone/structure. Variants can also comprise the substitution or coupling with parts of other molecules or coupling with other molecules.
Amino acid substitutions comprise conservative as well as non conservative replacement by other amino acids or by isosteres (modified amino acids that bear close structural and spatial similarity to protein amino acids), amino acid additions or isostere additions.
Conservative amino acid substitutions typically relate to substitutions among amino acids of the same class. These classes include, for example,                amino acids having uncharged polar side chains, such as asparagine, glutamine, serine, threonine and tyrosine;        amino acids having basic side chains, such as lysine, arginine, and histidine;        amino acids having acidic side chains, such as aspartic acid and glutamic acid; and        amino acids having nonpolar side chains, such as glycine, alanine, valine, leucine, isoleucine, proline, phenylalanine, methionine, tryptophan, and cysteine.        
Variant Proteins of Factor IX
In a preferred embodiment of the present invention a variant of the vitamin K-dependent serine protease factor IX (F.IX) or activated factor XI (F.IXa) is provided, wherein the variant of F.IX is characterized in that it has clotting activity in absence of its cofactor, wherein the cofactor is factor VIII (F.VIII) or activated factor VIII (F.VIIIa).
Factor IX (F.IX) within this patent application refers to the human F.IX protein and cDNA described by Kurachi and Davie, 1982.
Refseq NM_000133 for mRNA/cDNA (SEQ ID NO. 1), and
Refseq NP_000124 for protein sequence (SEQ ID NO. 2).
The amino acid sequence of SEQ ID NO. 2 contains the signal peptide and the pro-peptide of F.IX. The actual numbering starts at −46(Met); +1 is Tyr.
There are several naturally occurring polymorphisms in the gene as well as the amino acid sequence of F. IX. A list from the Hemophilia B Mutation Database, King's College London is shown below. For example, the most frequent polymorphism is at position 147 where threonine can be found in 67% and alanine in 33% of the population. Interestingly, the less frequent alanine is present in the only available recombinant F. IX therapeutic.
NameNuc NoBase ChangeAA_ChangeFrequency−1186C→T52%−793G→A44%MseI−698C→T44%BamHI(i)−561T→G 6%25A→GReported once37G→A−44, R→HReported once48A→T−40, I→FReported once181C→Arare192A→G19%353C→Trare709A→Grare1778C→T3/102627T→C6/103747C→A6/103756T→C6/10TaqI(iii)3797C→T6/103905A→T6/10DdeI5505−5076%6550G→CReported once6575C→Gpolymorphic inBrazilPointe-a-Pitre6596G→TReported once(Guadeloupe)XmnI7076G→71%TaqI(ii)9731?Reported once10512A→GReported 5 timesTaqI(i)11111T→65%13275C→T1/10MspI15625A→G78%17397T→G1/1020002C→A4/10MnlI (Malmo)20421G→A147, A→T33%20512T→C178, F→LReported once27731C→G5/1028364T→Crare29335G→A1/1029497G→T1/1029509T→Crare29532C→T4/1029648G→A4/1029650A→Grare30134T→C227, V→VReported 7 times30802+AReported 4 times30890C→T257, H→YReported 3 times31012C→T297, N→NReported once31093G→A324, Q→QReported once31103G→A328, V→IReported once32770T→C19%32847T→C“c” allelefrequent;“t” alleleseen 4 times
Activated factor IX (F.IXa) within this patent application refers to the activated F.IX molecule through cleavage of the 35 amino acid activation peptide as described above.
Since both coagulation factors F.IX and F.VIII always have to be activated before they can exhibit their function both F.IX/F.IXa or F.VIII/F.VIIIa can be used as synonyms.
For the numbering of the amino acid residues the F.IX numbering system is used (according to Kurachi and Davie, 1982, except when indicated otherwise. By some authors in the art, the chymotrypsinogen numbering is used for the description of certain amino acids in homology to the serine protease chymotrypsin. For the present invention the chymotrypsin numbering is only used when explicitly indicated herein.
The “clotting activity” or “functional activity” of F.IX can also be referred to as specific F.IX activity, which is usually measured in Unit/milligram (U/mg). Since one Unit (1 U) of F.IX is referred to as the amount of F.IX in 1 milliliter (ml) of normal human plasma, which corresponds to 5000 ng F.IX, the usual specific activity is around 200 U/mg. Since the specific activity of F.IX is defined as protease activity in the plasma in presence of F.VIII, there is no definition in use in the art for (clotting) activity in absence of cofactor F.VIII. Therefore, the clotting activity in absence of F.VIII, also called “F.VIII-like activity”, is expressed herein as percentage of the activity, which an equal amount of wild type F.IX would exhibit in the presence of F.VIII.
Thus, a F.IX variant has “clotting activity” in absence of its cofactor, when it corrects the blood coagulation deficiency caused by the absence of clotting F.VIII in the blood, which in case of a disease can either be due to absence of the F.VIII protein, presence of a defective F.VIII protein, or inhibition of the F.VIII protein, for example by inhibitory antibodies.
The assay system used in the present invention for determining “clotting activity” or “functional activity” of the variants of a vitamin K-dependent serine protease of the coagulation cascade, preferably of F.IX variants, is an one stage assay based on the aPTT. The activated partial thromboplastin time (aPTT or APTT) is a performance indicator measuring the efficacy of both the “intrinsic” (now referred to as the contact activation pathway) and the common coagulation pathways. Apart from detecting abnormalities in blood clotting, it is also used to monitor the treatment effects with heparin, a major anticoagulant. For the determination of the F.VIII or F.IX activity levels in a sample, the test is performed by spiking the sample into F.VIII or F.IX deficient plasma for measurement of the F.VIII or F.IX activity, respectively. This test is referred to as F.VIII or F.IX one stage assay. Now, F.VIII independent activity of a FAX variant can be determined by one stage assay and using F.VIII deficient plasma.
Briefly, blood is collected with oxalate or citrate which arrest coagulation by binding calcium. The plasma is separated from the corpuscular parts of the blood by centrifugation. In the case of recombinantly expressed and purified proteins, the protein is diluted in imidazole buffer. The sample is mixed and added to standardized factor (VIII or IX) deficient plama. In order to activate the intrinsic pathway, phospholipid, an activator (such as silica, celite, kaolin, ellagic acid), and calcium (to reverse the anticoagulant effect of the oxalate) are mixed into the plasma sample. The time is measured until a thrombus (clot) forms. The test is termed “partial” due to the absence of tissue factor from the reaction mixture (see Langdell et al., 1953).
Preferably, the variants of faxtor IX according to the invention have clinical relevant clotting activity (or clotting activity with clinical relevance), i.e. clotting activity which makes the variants suitable for clinical applications, as disclosed herein below.
A preferred clotting activity with clinical relevance is 1% or more clotting activity of the variant in absence of cofactor F.VIII, wherein 100% refers to the activity of wild type F.IX in presence of cofactor F.VIII or F.VIIIa.
Around 1% sustained factor VIII or factor IX levels are enough in prophylactic treatment regimens to prevent major bleeding complications in severe hemophilia patients. To reach a 1% level in a severe hemophilia A patient with a factor IX variant which has “1% F.VIII-like” activity in absence of F.VIII, F.IX variant levels of 100% of normal (around 5000 ng/ml) additional to the already physiologically present F.IX would be necessary. Such a treatment seems feasible and therefore the clinically relevant “factor VIII-like” activity is estimated at 1%.
In an embodiment the variant factor IX of the invention comprises a modification of the 99-loop, preferably by amino acid substitutions, insertions and/or deletions. A modification of the 99-loop can also be achieved by affecting the loop structure by amino acid substitutions, insertions and/or deletions of adjacent amino acid residues or residues interacting otherwise with the 99-loop.
The 99-loop or insertion loop 80-90 (according to chymotrypsinogen numbering) of factor IX encompasses amino acid residues 256 to 268 (F.IX numbering). The 99-loop is positioned near the active site and plays a role in the activation of F.IX. According to Sichler et al. (2003), Tyr-177 locks the 99-loop in an inactive conformation which, in the physiologic complex, is released by cofactor F.VIIIa. F.X is then able to rearrange the unlocked 99-loop and subsequently binds to the active site cleft.
The variant factor IX according to the invention comprises preferably at least one amino acid substitution in a position selected from the group of
265, 4, 338, 377, 259, 345, 1, 10, 37, 50, 85, 116, 119, 120, 181, 217, 235, 245, 253, 259, 301, 360, 383, 340, 86, 25, 34, 290, 291, 274, 353, 358, 375, 388, 35,
preferably K265T, G4Y, R338A, S377W, Y259F, Y345T, Y1A, V10K, R37T, Q50P, D85A, R116A, R119A, N120A, V181I, V217L, E235K, E245V, V253I, Y259F, K301I, S360A, I383V, T340S, V86A, F25Y, N34D, I290L, A291P, E274K, F353Y, R358A, G375F, E388G, T35D, and/or a modification of the 99-loop,
or preferably 265, 4, 338, 377, 259, 345, 1, 10, 37, 50, 85, 116, 119, 120, 181, 217, 235, 245, 253, 259, 301, 360, 383, 340, 86, 25, 34, 290, 291, 274, 353, 358, 375, 388, 35, 277,
or preferably K265T, K265A, G4Y, R338A, R338L, S377W, Y259F, Y345T, Y1A, V10K, R37T, Q50P, D85A, R116A, R119A, N120A, V181I, V217L, E277A, E235K, E245V, V253I, Y259F, K301I, S360A, I383V, T340S, V86A, F25Y, N34D, I290L, A291P, E274K, F353Y, R358A, G375F, E388G, T35D, and/or a modification of the 99-loop.
Preferably, the variant factor IX according to the invention comprises at least one amino acid substitution in a position selected from the group of 255 to 269, 383, 181, 290, 388, 34, 25, 353, 358, 338, 377, 4, 86, 217, 277, and/or a modification of the 99-loop.
More preferably, the variant factor IX comprises at least an amino acid substitution selected from K265T, I383V, V181I, I290L, E388G, N34D, F25Y, F353Y, R358A, R338A, R338L, S377W, G4Y, V86A, V217L, E277A and/or a modification of the 99-loop.
In a preferred embodiment, the variant factor IX comprises an amino acid substitution in position 265 (position 98 according to chymotrypsinogen numbering), preferably K265T (K98T according to chymotrypsinogen numbering) or, preferably, an amino acid substitution in position 265 which is selected from K265T, K265A, K265G, K265V, K265N and K265D.
In a preferred embodiment, the variant factor IX comprises an amino acid substitution in position 265 (preferably selected from K265T, K265A, K265G, K265V, K265N and K265D) or the amino acid substitution K265T (K98T according to chymotrypsinogen numbering) in combination with a further amino acid substitution.
The further amino acid substitution is preferably an (more preferably at least one) amino acid substitution in a position selected from the group of
4, 338, 377, 259, 345, 1, 10, 37, 50, 85, 116, 119, 120, 181, 217, 235, 245, 253, 259, 301, 360, 383, 340, 86, 25, 34, 290, 291, 274, 353, 358, 375, 388, 35 and/or 277,
more preferably selected from the group of:
383, 181, 290, 388, 34, 25, 353, 358, 338, 377, 4, 86, 217 and/or 277.
More preferably, the variant factor IX comprises the amino acid substitution K265T and an amino acid substitution selected from I383V, V181I, I290L, E388G, N34D, F25Y, F353Y, R358A, R338A, R338L, S377W, G4Y, V86A, V217L and/or E277A.
More preferably, the variant factor IX comprises an amino acid substitution in position 265 or the amino acid substitution K265T and (in combination with) an amino acid substitution selected from I383V, V181I, I290L, E388G, N34D, F25Y, F353Y, R358A, R338A, R338L, S377W, G4Y, V86A, V217L and/or E277A.
In a further preferred embodiment of the invention the variant factor IX comprises multiple amino acid substitutions from the group of amino acid positions 265, 4, 338, 377, 259, 345, 1, 10, 37, 50, 85, 116, 119, 120, 181, 217, 235, 245, 253, 259, 301, 360, 383, 340, 86, 25, 34, 290, 291, 274, 353, 358, 375, 388, 35, 277,
wherein “multiple amino acid substitutions” refers to substitutions in 2, 3, 4 or more positions.
Basis F.IX Variant (Group A)
The inventors have found a F.IX variant which allows F.VIII-independent therapy of bleeding disorders: a variant with an amino acid substitution in position 265, preferably K265T (K98T according to chymotrypsin numbering). K265T has been described in a different context in Sichler et al. 2003. Kolkman and Mertens (2000) describe a K265A variant.
The mutations/variations of F.IX assessed by the inventors are based on the observation that F.IXa has a poor activity compared to other serine proteases like F.Xa. In fact, exchanging only few amino acids affecting the 99-loop of F.IX by corresponding F.X sequences resulted in a dramatic improvement of amidolytic activity (up to several thousand-fold) in kinetic studies with truncated recombinant F.IXa variants using peptide substrates (see Hopfner et al., 1997 and Sichler et al., 2003)). At the same time a shift in specificity towards a “F.X-like” function was observed. Since these studies model F.IXa in a form not assembled to the intrinsic tenase complex, the inventors hypothesized that a variant protein with the same mutations could enable intrinsic propagation of the clot formation in absence of F.VIII. To test this the inventors introduced the mutations Y259F/K265T/Y345T (FTT) into F.IX and expressed the protein in tissue culture. Basically no effect was seen on F.IX specific activity; however the activity in F.VIII-deficient plasma increased dramatically.
Kolkman and Mertens (2000) already mentioned that a variant 1(265A could increase F.VIII-independent F.IX activity by a factor of 20. However, the tested F.IX Y259F/K265T/Y345T resulted in 2% activity at normal (100%) antigen levels in absence of F.VIII (FIG. 2). Considering that the presence of F.VIII increases F.IX activity by a factor of 106, the triple mutant resulted in an 20,000-fold increase in F.VIII-independent activity. This puts the clotting activity of the variant in absence of F.VIII in a range, in which this would also have physiological importance at the moment of clot formation or as possible therapeutic. Since this activity is still a small fraction of the F.IX-specific activity in presence of F.VIII (100% of F.IX antigen corresponds to 2% of “F.VIII-like” activity, i.e. “clotting activity in absence of cofactor F.VIII”), the inventors included additional mutations chosen by structural properties and homology comparisons of other serine proteases. They further tested the mutations Y259F, K265T, and Y345T independent from each other and could identify a single amino acid mutation (K265T, i.e. K98T in chymotrypsin numbering) which resulted in an enzyme with 191% F.IX and 6.7% “F.VIII-like” clotting activity and determined that the other single mutations are only decreasing the protease activity in presence and absence of F.VIII. (see Table 1)
Thus, in a preferred embodiment the variant factor IX is characterized that it has clotting activity in absence of cofactor F.VIII and has the K265T amino acid substitution.
The inventors have shown that position 265 is the main determinant for F.VIII bypassing activity of F.IX variants. The inventors showed that reversing residue 265 from T to the natural occurring K (V181I/265K/I383V, IKV) resulted in a near complete loss of F.VIII independent activity. Surprisingly, other amino acid substitutions, especially in the variants K265A/V181I/I1383V, K265G/V181I/I383V, K265N/V181I/I383V, K265N/V181I/I1383V, or K265D/V181I/I383V, resulted in similar F.VIII-bypassing activity than K265T/V181I/I383V, being highest for K265A/V181I/I383V. This result was unexpected, since the F.VIII independent activity for a factor IX variant carrying the single K265A substitution which was previously described was in a far lower range (Kolkman and Mertens, 2000).
Therefore, in a further preferred embodiment, the variant factor IX is characterized that it has clotting activity in absence of cofactor F.VIII and has an amino acid substitution in position 265, preferably selected from K265T, K265A, K265G, 1(265V, K265N and K265D or other amino acids.
However, the present invention does not encompass a variant factor IX that only has the amino acid substitution K265A. According to the present invention, if amino acid substitution K265A is present in a variant factor IX this implies that the variant has further amino acid substitutions in combination with K265A, i.e. it comprises further amino acid substitutions, such as in positions 181 and/or 383.
The inventors have furthermore found that the protein activity of F.IX can be even further modified by introduction of additional amino acid substitution to the amino acid substitution of Group A in order to obtain a F.IX variant with desired properties:
Amino acid positionAmino acid substitutionGroup A265K265Tor other amino acidsubstitution (preferablyselected from K265T,K265A, K265G, K265V,K265N and K265D)but not K265A aloneGroup B383, 181, 290I383V, V181I, I290LGroup C388, 34, 25, 353, 358, 383E388G, N34D, F25Y,F353Y, R358A, I383VGroup D338, 377, 4, 86, 217, 277R338A, R338L, S377W,G4Y, V86A, V217L, E277A
Modification of the preferred amino acid positions above (e.g. by amino acid substitution) can be combined with each other, preferably in the following way. However, further combinations are possible.    Group A alone—clotting activity in absence of cofactor F.VIII (F.VIII-independent activity)            increased compared to wild type            Group D alone—increased clotting activity in presence of cofactor F.VIII (F.VIII-dependent activity)            increased compared to wild type            Group A+B—clotting activity in absence of cofactor F.VIII            wherein the F.VIII-independent clotting activity is increased compared to the respective clotting activity of the basis variant (Group A).            Group A+C—clotting activity in absence of cofactor F.VIII and decreased activity in presence of cofactor F.VIII            wherein the F.VIII-dependent activity is decreased compared to wild type and preferably to the respective activity of the basis variant (Group A).            Group A+B+C—clotting activity in absence of cofactor F.VIII and decreased clotting activity in presence of cofactor F.VIII            wherein the F.VIII-independent clotting activity is increased compared to the respective clotting activity of the basis variant (Group A) and        wherein the F.VIII-dependent activity is decreased compared to wild type and preferably to the respective activity of the basis variant (Group A).            Group A+D—clotting activity in absence of cofactor and increased clotting activity in presence of cofactor            wherein the F.VIII-dependent activity which is increased compared to wild type and preferably to the respective activity of the basis variant (Group A).            Group A+B+D—clotting activity in absence of cofactor and increased clotting activity in presence of cofactor            wherein the F.VIII-independent clotting activity is increased compared to the respective clotting activity of the basis variant (Group A)        wherein the F.VIII-dependent activity which is increased compared to wild type and preferably to the respective activity of the basis variant (Group A).        
With the intention to generate F.IX variants with highest possible activity in absence of F.VIII, the inventors further added two additional amino acid substitutions (Group B), resulting in a protein (V181I/K265T/I383V) with 167% F.IX and 16% “F.VIII like” activity. The variant accordingly has a 160,000-fold higher clotting activity in absence of F.VIII compared to the wild type protein. These additional amino acid substitutions were chosen in a way to maximally increase F.VIII independent F.IX activity without exorbitantly increasing the F.IX specific activity. The rationale behind this approach was that too much F.IX specific activity in presence of F.VIII might increase the risk of thrombotic complications and therefore pose a concern for using the proposed F.IX variants as therapeutic. Also other combinations of the above listed amino acid substitutions are possible, for example amino acid substitutions from Group C can further restrict the activity of a variant protein in presence of F.VIII while only minimally affecting the activity in absence of F.VIII. Similarly, the activity in both, presence and absence of F.VIII, can be improved using amino acid substitutions from Group D. In this way a variant with the five mutations V181I/K265T/R338A/S377W/I383V was generated which exhibits increased activity in absence of F.VIII (22% “F.VIII like” activity corresponding to 220,000-fold higher then wild type F.IX) and in presence of F.VIII (16-fold higher compared to wild type F.IX). The FIX and “FVIII like” activities of tested variants are illustrated in Table 1.
The possibility of these further modifications is important since it allows the design and tailoring of F.IX variants for specific applications, such as
(1) Low F.IX activity in presence of F.VIII (F.VIII-dependent activity) while high F.IX activity in absence of F.VIII (F.VIII-independent activity) (i.e. Groups A+C) is desired to decrease thrombogenicity of a therapeutic to treat hemophilia A or patients with inhibitory antibodies against F.VIII.
(2) A protein with high protease activity independently of presence of F.VIII or F.IX might have the potential to treat all types of F.IX or F.VIII deficiencies ((i.e. Group A+B+D).
Since the effects of the listed single amino acid substitutions is of differentiated strength with respect to their effect on F.IX activity in absence or presence of F.VIII, also amino acid substitutions from different Groups can be combined to achieve a desired over all effect on F.IX activity for specific applications. For example, combining the 1(265T variant (Group A) with the amino acid substitutions V181I and I383V (Group B), results in a protein with high activity in absence of F.VIII, but basically normal activity in presence of F.VIII, corresponding to application (1). For details please see Table 1.
All variants of Group A and in combination of Group A are especially suitable for the therapy of patients with hemophilia A, inhibitory antibodies and other bleeding disorders as well as for the treatment of hemophilia B.
In more detail:                FIX variants which in combination with the basis variant further increase clotting activity in absence of F. VIII (Group A combined with Group B)        
In this preferred embodiment of the invention, a variant factor IX is characterized in that it has clotting activity in absence of cofactor F.VIII,
and comprises at least one amino acid substitution in a position selected from the group of 265, 383, 181 and 290.
Preferably, the variant factor IX comprises the amino acid substitution K265T and amino acid substitution(s) in a position selected from the group of 383, 181 and/or 290 (group B), more preferably comprises the amino acid substitution K265T and amino acid substitution(s) selected from I383V, V181I and/or I290L.
Preferably, the variant factor IX comprises an amino acid substitution in position 265 or the amino acid substitution K265T, in combination with amino acid substitution(s) in a position selected from the group of 383, 181 and/or 290 (group B),
more preferably comprises an amino acid substitution in position 265 or the amino acid substitution K265T and amino acid substitution(s) selected from I383V, V181I and/or I290L.
An amino acid substitution in position 265 is preferably selected from K265T, K265A, K265G, K265V, K265N and K265D.
These F.IX variants of Group A+B have a F.VIII-independent clotting activity which is increased compared to the respective clotting activity of the basis variant (Group A).                FIX variants which in combination with the basis variant restrict the clotting activity in presence of F. VIII (Group A combined with Group C)        
In this preferred embodiment of the invention, a variant factor IX is characterized in that it has clotting activity in absence of cofactor F.VIII, but decreased activity in presence of cofactor F.VIII,
and comprises at least one amino acid substitution in a position selected from the group of 265, 383, 388, 34, 25, 353 and/or 358.
Preferably, the variant factor IX comprises the amino acid substitution K265T and amino acid substitution(s) in a position selected from the group of 388, 34, 25, 383, 353 and/or 358 (Group C),
more preferably comprises the amino acid substitution K265T and amino acid substitution(s) selected from E388G, N34D, F25Y, F353Y, I383V and/or R358A.
These F.IX variants of Group A+C have a F.VIII-dependent activity which is decreased compared to wild type and preferably to the respective activity of the basis variant (Group A) (or preferably decreased compared to variant(s) of Group A+B). Thus, these F.IX variants of Group A+C restrict F.VIII-dependent activity and minimize possible thrombogenic risks.                FIX variants which in combination with the basis variant further increase clotting activity in absence of F. VIII as well as restrict the clotting activity in presence of F. VIII (Group A combined with Group B and Group C)        
In this preferred embodiment of the invention, a variant factor IX is characterized in that it has clotting activity in absence of cofactor F.VIII, but decreased activity in presence of cofactor F.VIII
and comprises at least one amino acid substitution in a position selected from the group of 265, 383, 181, 290, 388, 34, 25, 353 and/or 358,
Preferably, the variant factor IX comprises the amino acid substitution K265T and amino acid substitution(s) in a position selected from the group of 383, 181, 290, 388, 34, 25, 353 and/or 358 (group B+C),
more preferably comprises the amino acid substitution K265T and amino acid substitution(s) selected from I383V, V181I, I290L, E388G, N34D, F25Y, F353Y and/or R358A.
These F.IX variants of Group A+B+C combine the characteristics of the three groups:                they have F.VIII-independent clotting activity,        they have a F.VIII-independent clotting activity which is increased compared to the respective clotting activity of the basis variant (Group A) and        they have a F.VIII-dependent activity which is decreased compared to wild type and preferably to the respective activity of the basis variant (Group A) (or preferably decreased compared to variant(s) of Group A+B).        
Thus, these F.IX variants of Group A+B+C increase F.VIII-independent activity, restrict F.VIII-dependent activity and minimize possible thrombogenic risks.                Variant proteins of factor IX with increased clotting activity in presence of cofactor F. VIII        
(Group D)
In a further aspect of the present invention, a variant of factor IX (F.IX) is characterized in that it has increased clotting activity in presence of its cofactor compared to wild type, wherein the cofactor is factor VIII (F.VIII) or activated factor VIII (F.VIIIa).
A variant factor IX according to this aspect of the present invention comprises at least one amino acid substitution in a position selected from the group of 338, 377, 4, 86, 217 and/or 277,
more preferably comprises at least one amino acid substitution selected from R338A, R338L, S377W, G4Y, V86A, V217L and/or E277A.
The variants of Group D and variants that are combined with Group D are especially suitable for the treatment of hemophilia B.
A protein with isolated high F.IX activity in presence of F.VIII is a good therapeutic for the treatment of F.IX deficiency. For this purpose, no high activity in absence of F.VIII, i.e. Group A, such as mutation K265T, is required. The amino acid subsitutions of Group D also increase F.IX activity in presence of F.VIII in absence of the above mentioned K265T mutation (Group A). A list of variants tested for this purpose without introduction of the K265T mutation are shown in Table 2.                Variant proteins of factor IX with clotting activity in absence of cofactor and increased clotting activity in presence of cofactor (Group A combined with Group D)        
In this preferred embodiment of the invention, a variant factor IX is characterized in that it has clotting activity in absence of cofactor F.VIII and increased clotting activity in presence of cofactor F.VIII compared to wildtype,
and comprises at least one amino acid substitution in a position selected from the group of 265, 338, 377, 4, 86, 217 and/or 277.
Preferably, the variant factor IX comprises the amino acid substitution K265T and amino acid substitution(s) in a position selected from the group of 338, 377, 4, 86, 217 and/or 277 (group D),
more preferably comprises the amino acid substitution K265T and amino acid substitution(s) selected from R338A, R338L, S377W, G4Y, V86A, V217L and/or E277A.
These F.IX variants of Group A+D have a F.VIII-dependent clotting activity which is increased compared to the respective F.VIII-dependent clotting activity of wild type, and preferably of the basis variant (Group A). They have also an increased potency for treatment of hemophilia B.                Variant proteins of factor IX with increased clotting activity in absence as well as in presence of cofactor (Group A combined with Group B and Group D)        
In this preferred embodiment of the invention, a variant factor IX is characterized in that it has (increased) clotting activity in absence of cofactor F.VIII and increased clotting activity in presence of cofactor F.VIII,
and comprises at least one amino acid substitution in a position selected from the group of 265, 383, 181, 290, 338, 377, 4, 86, 217 and/or 277.
Preferably, the variant factor IX comprises the amino acid substitution K265T and amino acid substitution(s) in a position selected from the group of 383, 181, 290, 338, 377, 4, 86, 217 and/or 277,
more preferably comprises the amino acid substitution K265T and amino acid substitution(s) selected from I383V, V181I, I290L, R338A, R338L, S377W, G4Y, V86A, V217L and/or E277A.
These F.IX variants of Group A+B+D combine the characteristics of the three groups:                they have F.VIII-independent clotting activity,        they have a F.VIII-independent clotting activity which is increased compared to the respective clotting activity of the basis variant (Group A) and        they have a F.VIII-dependent activity which is increased compared to wild type and preferably to the respective activity of the basis variant.        
The variant factor IX according to the invention is more preferably selected from                variant K265T,        variant K265T/V181I,        variant K265T/I383V,        variant K265T/V181I/I383V,        variant K265T/V181I/I383V/R338A/S377W,        variant K265T/V181I/I383V/E388G,        variant K265T/V181I/I290L/I383V,        variant K265T/V181I/I290L/I383V/E388G,        variants comprising R338A and S377W.        
More preferably, the variant factor IX according to the invention is                variant K265T,        variant K265T/V181I,        variant K265T/I383V,        variant K265T/V181I/I383V, or        variant K265T/V181I/I383V/R338A/S377W.        
In a preferred embodiment, the variant factor IX according to the invention is selected from variant K265T or                a variant with an amino acid substitution in position 265 (preferably selected from K265T, K265A, K265G, K265V, K265N and K265D),        
preferably in combination with an amino acid substitution in position 181 and/or 383 (preferably V181I and/or I383V),
More preferably, the variant factor IX according to the invention is                variant K265T/V181I/I383V,        variant K265A/V181I/I383V,        variant K265G/V181I/I383V,        variant K265V/V181I/I383V,        variant K265N/V181I/I383V, or        variant K265D/V181I/I383V.        
The expression, for example, “K265T/V181I/I383V” refers to a variant containing these amino acid substitutions in combination, i.e. K265T and V181I and I383V in combination. The expression “K265T/V181I/I383V/R338A/S377W” refers to a variant containing these amino acid substitutions in combination, i.e. K265T and V181I and I383V and R338A and S377W in combination, and so one.
Disclaimer:
The present invention does not encompass a variant factor IX that only has the amino acid substitution K265A. According to the present invention, if amino acid substitution K265A is present in a variant factor IX this implies that the variant has further amino acid substitutions in combination with K265A, i.e. it comprises further amino acid substitutions, such as in positions 181 and/or 383.
Furthermore, the present invention does not encompass a variant factor IX that only has the following amino acid substitution(s):
FTT (Y259F/K265T/Y345T);
Y259F/K265T;
V181F;
R338A.
Also, the following variants of factor IX are not encompassed by the present invention:
Y259F/A261K/K265T/Y345T
Y259F/K265T/Y345F/I383V/E388G
Y259F/A261K/K265T/Y345F/I383V/E388G
Modification of the 99-loop has been attempted repeatedly as strategy to modify F.IX activity (Hopfner et al., 1997, Sichler et al., 2003). The most promising variants Y259F (/A261K) and K265T) have been further investigated for possible activity in absence of F.VIII (Hartmann et al., 2007 as well as WO 2008/092644 and WO 2008/092643). The idea behind this approach was to modify the conformation of the F.IX specific 99-loop by changing residues at both ends of the loop. The surprising finding in our investigation was that in contrast to the F.IX models described, in which F.IX was partially truncated and/or produced in bacteria instead of eukaryotic cells, the F.VIII independent activity solely depends upon mutation at position 265. Further more, the mutation at position Y259F was hindering the F.VIII independent and overall activity and only excluding the mutation at position Y259F high enough F.VIII independent activities could be obtained to further pursue an approach using F.IX variants as therapeutics.
In case of the mutations I383V and E388G, the case was similar. Both mutations were seen as a unit in the first description by Hopfner et al. (1997) and later on by the descriptions from Baxter (see Hartmann et al., 2007 as well as WO 2008/092644 and WO 2008/092643)). Hopfner et al. (1997) even reported that I383V only had a moderate effect in the bacterial F.IX expression system and therefore was propagated only in combination with E388G. Our experiments suggest the contrarian. Only the mutation I383V added to the F.VIII independent F.IX activity, while E388G was disturbing the activity. We believe that these differences are crucial for potential development of a new F.IX based bypassing agent. First of all, the activities necessary to improve hemostasis are improved by several fold excluding these mutations, and secondary, the numbers of mutations introduced into F.IX will be the main safety concern, since the risk of the formation of inhibitory antibodies to F.IX probably would increase with the amount of changes which are introduced into the protein.                Conjugates        
In a preferred embodiment, the variants of factor IX according to the invention comprise a further compound or moiety, which is preferably covalently attached to the variant (conjugate).
Preferably, the further compound or moiety is selected from                a protein, such as albumin,        a label, such as chromophor, fluorophor, isotope,        
and/or                a polymer, such as PEG.        
Nucleic Acids of the F.IX Variants and Pharmaceutical Compositions
According to the present invention the above object is furthermore solved by providing nucleic acids encoding the variant factor IX according to the present invention.
A “nucleic acid” refers to DNA, RNA and derivatives thereof, DNA and/or RNA comprising modified nucleotides/nucleosides.
Preferably, the nucleic acid is operably linked to a promoter and/or terminator sequence. Preferred promoter and/or terminator sequences are the human alpha1 anti-trypsin promoter, the hepatic locus control region 1, or the cytomegalovirus promoter and a polyadenylation signal vom human or bovine growth hormone of the Simianese Virus 40.
The skilled artisan is able to select suitable promoter and/or terminator sequences.
A nucleic acid is “operably linked” to a promoter and/or terminator sequence when the transcription/translation of the nucleic acid is controlled by the respective promoter/terminator, preferably in a cell and by the cellular transcription/translation machinery, such that e.g. the encoded protein can be obtained from the nucleic acid.
Preferably, the nucleic acid is an expression plasmid, a gene therapy construct, a sequence encoded in a gene transfer vector, a gene sequence used for DNA modification or repair, or similar.
Preferred gene therapy constructs are viral and non-viral vectors, such as adeno-associated viral vectors (AAV), plasmid vectors, or minicircle vectors, as described e.g. in (Schuettrumpf et al., 2005).
According to the present invention the object is furthermore solved by providing a pharmaceutical composition comprising at least one variant of factor IX (F.IX) of the invention or at least one nucleic acid of the invention, and optionally pharmaceutically acceptable carrier(s) and/or excipient(s).
Suitable pharmaceutically acceptable carrier(s) and/or excipient(s) are known in the art. The skilled artisan will selected the preferred pharmaceutically acceptable carrier(s) and/or excipient(s) depending on the intended application of the pharmaceutical composition, such as disorder to be treated, patient to be treated, treatment regimen etc.
Medical Uses
According to the present invention the object is furthermore solved by providing the variants of a vitamin K-dependent serine protease of the coagulation cascade, most preferably the variants of factor IX, as disclosed in the present invention or the nucleic acids encoding them or the pharmaceutical compositions of the invention for the diagnosis, prevention and/or treatment of diseases.
The disease to be diagnosed, prevented and or treated is preferably a bleeding disorder or bleeding.
A “bleeding disorder” is preferably hemophilia A and/or hemophilia B, hemophilia caused or complicated by inhibitory antibodies to factor VIII, by a deficiency of factor VIII or factor IX, or by the presence of a non functional factor VIII or factor IX protein, or any other bleeding or bleeding tendency.
Preferably, the bleeding disorder is hemophilia A, hemophilia caused or complicated by inhibitory antibodies to factor F.VIII or F.VIIIa, hemophilia B.
Preferably, the bleeding disorder or bleeding is a bleeding disorder where by-passing agents are used, including e.g. neonatal coagulopathies; severe hepatic disease; high-risk surgical procedures; traumatic blood loss; bone marrow transplantation; thrombocytopenias and platelet function disorders; urgent reversal of oral anticoagulation; congenital deficiencies of factors V, VII, X, and XI; and von Willebrand disease with inhibitors to von Willebrand factor, blood loss in connection with large injuries, cerebral bleedings, thrombocyte function disorders.
According to the present invention the object is furthermore solved by using a variant of a vitamin K-dependent serine protease of the coagulation cascade, most preferably the variants of factor IX, as disclosed in the present invention or the nucleic acids encoding them for the manufacture of a medicament for the treatment and/or the prevention of a bleeding disorder or bleeding.
Preferably, the variant of factor IX (F.IX), the nucleic acid or the pharmaceutical composition of the invention are used for protein infusion therapy, cellular therapy, gene therapy and/or prophylaxis of a bleeding disorder or bleeding.
Diagnosis, prevention and/or treatment, wherein the disease is hemophilia A or hemophilia caused or complicated by inhibitory antibodies to factor F.VIII or F.VIIIa: preferably by                a variant of Group A, more preferably variant K265T        variants of Group A in combination with Group B and/or C and/or D                    Group A+B as defined herein            Group A+C as defined herein            Group A+B+C as defined herein            Group A+D as defined herein            Group A+B+D as defined herein                        the respective nucleic acids, pharmaceutical compositions.        
The inventors are the first to apply a variant of Group A, in particular K265T, for the treatment of hemophilia A or hemophilia caused or complicated by inhibitory antibodies to factor F.VIII or F.VIIIa.
The variant F.IX molecules with higher protease/clotting activity in absence of F.VIII could be an alternative to common bypassing agents, with the advantage of being activated directly at the site of injury. This would resemble physiologic clot formation, prevent the infusion of already activated proteases as usual in the available bypassing agents at the moment, and make therapy safer.
A zymogene F.IX variant would presumably also have a far longer half life, enabling prophylactic substitution therapy also in inhibitor patients. Intriguingly, patients lacking F.VIII could even be suitable for a gene transfer approach using the smaller and less immunogenic F.IX, for which gene therapy studies are far more promising at the moment. Thinking of the relatively small number of patients and the large efforts necessary bringing gene therapy for hemophilia into clinical praxis, the proposed F.IX variants could even bundle the efforts offering therapy for patients with hemophilia A and hemophilia B, or with inhibitory antibodies to F.VIII. Eventually, the variant would also be useful in the treatment of other bleeding disorders.
Another aspect of the described variants is, that without need for F.VIIIa and higher activity towards both, F.X cleavage and chromogenic substrate cleavage, the variants could be used in diagnostic testing systems or for the development and screening for direct F.IXa inhibitory substances, which since a long time are desired as anticoagulants, but for which no effective screening was possible, due to the low efficacy of F.IXa without assembly in the tenase complex.
Diagnosis, prevention and/or treatment, wherein the disease is hemophilia B, by all variants described herein preferably by                a variant of Group A, more preferably variant K265T        variants of Group A in combination with Group B and/or C and/or D                    Group A+B as defined herein            Group A+C as defined herein            Group A+B+C as defined herein            Group A+D as defined herein            Group A+B+D as defined herein                        a variant of Group D, more preferably variant K265T        variants of Group D in combination with Group A and/or B                    Group A+D as defined herein            Group A+B+D as defined herein                        the respective nucleic acids, pharmaceutical compositions.        
Diagnosis, prevention and/or treatment of a bleeding disorder or bleeding, wherein furthermore the thrombogenic risks are minimized preferably by                variants in combination with Group C                    Group A+C as defined herein            Group A+B+C as defined herein                        the respective nucleic acids, pharmaceutical compositions.        
Diagnosis, prevention and/or treatment of both, hemophilia A and B by all variants described herein except Group D alone.
Diagnosis, prevention and/or treatment of hemophilia A or hemophilia caused or complicated by inhibitory antibodies to factor F.VIII as well as hemophilia B, by all variants described herein except Group D alone.
The variants of the present invention are suitable tools to treat patients with bleeding disorder using protein administration, or cell- or gene therapeutic administration (viral, DNA, RNA, or other vectors). Diseases for treatment are hemophilia A and B, also caused or complicated by inhibitory antibodies to FVIII, for treatment of bleeding and for prophylactic therapy.
The inventors have shown that the variants of the present invention                correct clotting time in presence of inhibitory antibodies against F.VIII (confirming the function of the tested F.IX variants also in presence of high titers of F.VIII inhibitors),        correct coagulation in vivo (being the first evidence that F.IX variants can serve as hemostatically active therapeutics in vivo),        stop bleeding in presence of inhibitory antibodies against F.VIII (confirming the functionality of F.IX variants in both, in presence and in absence, of inhibitory antibodies to F.VIII).        
For further details, see Examples 6-8 and FIGS. 4-7.
Screening Method
According to the present invention, the object is furthermore solved by providing a method for screening of anticoagulant compounds (anticoagulants), preferably substances that directly inhibit F.IXa.
Such a method comprises the use of at least one variant factor IX of the present invention, as defined herein.
In such a method, no further components of the tenase complex are necessary (wherein “tenase” refers to complex of the activated forms of the blood coagulation factors factor VIII (F.VIIIa) and factor IX (F.IXa). It forms on a phospholipid surface in the presence of calcium and is responsible for the activation of factor X).
An advantageous aspect of the described variants is, that without need for F.VIIIa and higher activity towards both, F.X cleavage and chromogenic substrate cleavage, the variants are suitable tools in diagnostic testing systems or for the development and screening for direct F.IXa inhibitory substances, which since a long time are desired as anticoagulants, but for which no effective screening was possible, due to the low efficacy of F.IXa without assembly in the tenase complex.
A screening method according to the invention is preferably a method for identifying a compound which binds to a variant factor IX of the present invention and/or which modulates its activity,
preferably comprising the following steps:                providing compounds/substances to be tested,        providing at least one variant factor IX of the present invention,        contacting a compound/substance to be tested with the at least one variant factor IX of the present invention,        determining whether the compound/substance binds to the at least one variant factor IX,        optionally, determining whether the compound/substance modulates the activity of the at least one variant factor IX.        
The following examples and drawings illustrate the present invention without, however, limiting the same thereto.